During production of fibre pulp from lignocellulosic materials by modern grinding processes, large quantities of steam are produced which must be evacuated from the grinding process in such manner that the flow of the materials through the grinding apparatus remains undisturbed. As explained in U.S. patent application Ser. No. 808,713, it is known to utilize the heat content of the steam by discharging it at as high a pressure as possible without disturbing the actual process of fibre production. This is achieved by feeding the fibre pulp together with the processing steam into a pressure cyclone in which a steam-pressure considerably higher than atmospheric pressure is maintained. The steam separated from the pulp in the pressure cyclone may then be conveyed at an equivalent pressure to other production steps requiring the use of steam at superatmospheric pressures.
A pressure cyclone of this type, especially as designed for the separation of high-pressure steam from fibre pulp, is provided with an entrance duct for the fibre pulp, an escape duct for the steam separated from the pulp and a screw conveyor for transporting the fibre pulp from which the steam has been removed, to the exit duct to which is connected a device for discharging the separated pulp allowing a steam-pressure to be maintained in the cyclone substantially higher than atmospheric pressure. This discharge device may be some form of vapour-tight feeder, such as a high-density pump (gear pump), cell feeder, etc.
However, it now appears that difficulties may arise as the fibre pulp is discharged from the pressure cyclone in that blockages may occur in the exit duct of the screw conveyor just before the discharging device, causing the screw itself to be stuck. The principal objective of the present invention is to achieve a simple device for eliminating the risk of the screw being stuck.